The octogenarian opened fire when two men, aged 74 and 78, came upon him trying to set fire to the door of the mosque
A 84-year-old man shot and seriously wonded two men in their 70s saw him trying to burn a mosque in southwest France. The government expressed its solidarity.
The man is a former candidate for France's ultra-right party, reports France 24.
The octogenarian opened fire when two men, aged 74 and 78, came upon him trying to set fire to the door of the mosque in Bayonne on Monday afternoon, a police statement said.
The victims were brought to a nearby hospital with serious injuries, while the suspected shooter was later arrested near his home. He had also set fire to a car outside the Mosque.
Police identified the man as Claude Sinke, and said he had admitted to being the shooter.
Sinke stood as a candidate for Marine' le Pen's National Front in 2015 regional elections, according to the official list.
Interior Minister Christophe Castaner offered his "solidarity and support to the Muslim community" after the incident.
In a tweet, Castaner said the events "pain every one of us" and said he shared the "shock and horror" Muslims must be feeling.
Le Pen, for her part, spoke of an "attack" and described it as "an unspeakable act".
The man's actions were "absolutely contrary to the values of our movement," she tweeted.
The mosque has been cordoned off for investigations and a bomb squad was sent to Sinke's home in Saint-Martin-de-Seignanx, a town of 5,000 people some 16 kilometres (10 miles) from Bayonne.
A team of psychologists was put together to provide care for witnesses of the incident.
- Three weapons -
Police told AFP the man had three sub-military grade weapons, which he had voluntarily declared to investigators.
The incident came just hours after President Emmanuel Macron had urged France's Muslims to step up the fight against "separatism" in the wake of the latest attack by an Islamist radical on French soil, in which a police employee stabbed four colleagues to death this month.
There have been intermittent attacks on mosques in France since 2007, when 148 Muslim headstones in a national military cemetery near Arras were smeared with anti-Islamic slurs and a pig's head was placed among them.
In June this year, a gunman wounded an imam in a shooting at a mosque in the northwestern city of Brest, but police ruled out a terror motive.
In March, workers building a mosque in the small southwestern town of Bergerac found a pig's head and animal blood at the entrance to the site -- two weeks after a gunman killed 50 Muslims in Christchurch, New Zealand, in a shooting spree at two mosques.
Mosques were also targeted after the killing of 12 people at the Charlie Hebdo satirical magazine in 2015 by Islamist radicals. Dozens of mosques were attacked by arsonists at the time, others with firebombs, grenades or even gunfire.